This invention relates to transfer switches and more particularly to a system for converting a manual transfer switch into an automatic transfer switch.
Transfer switches are used for switching between multiple power supplies. Electrical equipment may be powered normally from a primary Alternating Current (A.C.) or Direct Current (D.C.) power supply. If the primary power supply goes down, the transfer switch switches out the primary power supply and switches in a secondary power supply to power the electrical equipment.
A manual transfer switch requires a system operator to manually throw one or more switches that disconnect the primary power supply from the electrical equipment and switch in the secondary power supply. An automatic transfer switch continuously senses the voltage levels of the power supplies. When a power outage on the primary power supply is detected, the automatic transfer switch then automatically switches out the primary power supply and automatically switches in the secondary power supply.
Electrical equipment may be installed initially with a manual transfer switch. Due to changing system requirements, it might then be necessary to replace the manual transfer switch with an automatic transfer switch. Replacement typically requires swapping out the entire electrical panel that holds both the manual transfer switch, electrical circuit breakers and other power circuitry. This replacement is prohibitively expensive and not cost effective especially when a large number of manual transfer switches have to be replaced.
Another problem exists when only a percentage of automatic transfer switches need to be installed, but may have to be installed at different locations at different times. This is particularly true in wireless cellular telephone systems that include hundreds of cell sites that each from time to time may require a backup power supply. Many cell sites have manual transfer switch systems that allow a portable power supply to power the cell site when a power outage occurs in the primary power supply.
Communication critical cell site locations, or difficult to access cell site locations, may need to be upgraded either permanently or temporarily with automatic transfer switches and a secondary power supply. This eliminates a technician from having to transport a portable power supply to these locations during power outages. The problem is that traffic patterns identifying critical cellular communication sites or chronically unreliable cell sites often cannot be determined until after the cell site is already up and running. Therefore, it cannot be determined which cell sites qualify for automatic power transfer switching until after the cell site is already installed with a manual transfer switch.
Accordingly, a need remains for quickly, inexpensively and reliably converting an operating manual transfer switch into an automatic transfer switch without a significant power outage.